The absorption of light and the colours of natural bodies / by Professor Stokes.

  • Sir George Stokes, 1st Baronet
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: The absorption of light and the colours of natural bodies / by Professor Stokes. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    examine it by a prism applied to the eye, you will, however, see that the violet, or more or less of the violet, is gone; instead of seeing as is usual the double line H, you will see . the fluid terminate, according to the strength of the solution and the thickness looked through, more or less towards the ! violet, say on an average about half way between the fixed ■ ] lines G and H. Now the incident rays work on the fluid in such a ' manner as to cause it to give out light of a different kind ] altogether ; a light which is found to be heterogeneous, or l to consist of rays of various degrees of refrangibility. This rule I find to be universal, namely, that the refrangibility of the light in this process is always lowered. I have | never found any exception to that, nor I believe has anyone | since.1 The rays which any one of these fluids is capable of giving out under the influence of these other rays are , always of lower refrangibility, and you never have the refrangibility raised. I will endeavour presently to show a test-tube with one of these solutions in part of the spectrum, though I cannot promise that it will be seen at a distance. The fact is I am accustomed to work with sunlight rather than with the electric light, and I require more preliminary trials than I allowed myself for making the thing succeed. Still I think you see that on interposing a test-tube with the solution of quinine in the beam from the electric lamp, aftei it has passed through the prism, it cuts off certain portions of the spectrum thrown on the wall beyond, forming a shadow which shows in what part of the rays proceeding to form the spectrum the tube is for the moment placed ; the blue light with which the solution glows, commencing about the violet, is seen altogether beyond the region of the visible rays. Here is a solution of a substance obtained from the bark of the horse-chestnut which shows it still better. \ ou observe the blue band beyond the visible spectrum altogether. Another instance is when we allow the beam of light to fall on a piece of red cloth, it shows an orange band beyond the visible rays. 1 efflorescence, ortho exhibition of light by a body intensely heated by the concentration upon it of invisible heat-rays is in some respects so different from the phenomena of fluorescence or phosphorescence that I do not reganl it as forming any exception to the rule.